1. Field of the Invention
The present invention relates to a management server, a base station, a communication system, and a communication method.
2. Description of the Related Art
A 3G mobile telephone service called the third generation was started in Japan in 2002. In the beginning, the main application was transmission of small packets such as sound and emails, but with the introduction of High Speed Downlink Packet Access (HSDPA) and the like, download of larger packets, such as download of music files or shared videos, has come to be performed.
As such, with the increase in the size of packets to be downloaded, wireless communications between a base station and a terminal were expanded, and HSPA+ service realizing maximum 21 Mbps was started. Furthermore, LTE that uses OFDMA in downlink is expected to start around 2010 and a 4G service is expected to start around 2015, and a world where maximum 1 Gbps is realized with a semi-fixed terminal and maximum 100 Mbps is realized in a mobile environment is becoming a reality.
To realize a wireless environment with a high communication rate as described above, it is assumed that cells will shift to microcells and picocells. Wireless environment of dead spots at the edge of a cell can be improved to a certain degree by placing relay stations, for example, but in the case resources of base stations are in short supply, the effect obtained by placing relay stations may be reduced.
Accordingly, in indoors having Fiber To The Home (FTTH), a high-speed data communication environment is anticipated to be realized without placing load on outdoor wireless resources, by placing small base stations called femtocell base stations.
Also, with respect to a white space which is an unused frequency band at a position or a region, it is becoming possible to use a frequency band in the white space without license if such frequency band can be decided to be not used. Therefore, it is expected that a technology for using a locally unused frequency band fairly and effectively will become important in the future.
Furthermore, a “special home zone” allowing frequency bands assigned to communications company to be freely used under the condition that no interference is caused to a public macrocell may possibly be permitted in the future. In such a case, the current configuration of femtocell base stations assuming operation in the frequency band assigned to each communications company may not be effective.
Thus, consideration is beginning to be given to a configuration of a base station that sets a frequency band in an autonomous, decentralized manner. For example, a configuration of storing frequency band information to be monitored in a base station, detecting receiving power of each frequency band, deciding that the use of a frequency band whose receiving power is at a threshold or less does not cause interference to a public macrocell, and using this frequency band as a carrier frequency is conceivable. Also, JP-A-2004-260371 discloses, as a centralized control structure, a repeater that sets a carrier frequency based on a frequency band which has been notified.